The present invention relates to circuits for monitoring the operation of other circuits, and more particularly to a circuit for monitoring the operating conditions of an electric load, such as a solenoic or an electrical heater for heating a stator of an electric motor or for heating a valve.
Nuclear power plants often employ emergency coolant flow valves which stand inoperative for long periods of time. Sometimes valves of this nature include intregral resistance heater coils to prevent the condensation of water in the valve and the subsequent deterioration in the operation of that valve. If the heater coil were to fail, no immediate changes would take place which would permit observation and corrections of the fault condition. Moreover, these circuits generally did not include electronic monitoring circuits for monitoring the operation of the heater coils to verify that they are, in fact, operating properly.
The patent to Tamasi, U.S. Pat. No. 3,744,046 discloses an engine heating system monitor for use on diesel truck tractors and the like which monitors the supply of current to the heater system. Indicator lights indicate whether the heater system is energerized or de-energized, and whether the heater is or is not drawing current.